A. Field of the Invention
The present invention relates generally to automatically powered vegetation trimmers, and more particularly to a novel ground guide system for the head of a powered trimmer which allows height adjustment and, in the case of cord- or filament-type trimmers, enables use of a bump feed mechanism common to such trimmers with or without the ground guide in place.
B. Description of the Prior Art
Automated trimmers of the prior art generally comprise a trimmer head at a distal end of a user handle, and are intended for free multi-directional movement of the trimmer head just above the ground to trim vegetation near obstacles such as trees, fences, and the like. Such automated trimmers commonly include a brush blade or a spool of filament cord mounted in the trimmer head for rotation at high r.p.m., whereby a free end of the cord extends tangentially outward from the spool to serve as a trimming means. The cord-type trimmers very often include a manual bump feed mechanism, for example as taught by U.S. Pat. No. 5,222,301, for advancing additional cord to restore the free end during use. The bump feed mechanism typically extends from the bottom of the trimming head and is actuated by momentarily bumping or impacting same against an environmental surface such as the ground.
A recognized drawback of automated trimmers of the type described above is that the height of the trimming means above the ground is constantly changing, resulting in an uneven cut. This is particularly true where the weight of the trimmer head overburdens the user's physical strength, as often happens with heavy-duty automated trimmers. A related problem is that of gouging, as may occur when the rotating trimming means is inadvertently allowed to contact the ground or other environmental surface.
In order to overcome the problems mentioned above, ground guide systems for powered trimmers have been proposed. U.S. Pat. No. 4,483,069, at FIG. 3 thereof, discloses a trimmer head including a "glide ball" having a smooth, downwardly facing convex surface. The glide ball is threadably mounted on the trimmer head beneath a rotating spool carrying trimming cord by an axially extending stud. The distance between the glide ball and the rotating spool is predetermined by the tightened threaded mating of the glide ball onto the stud, and there is no means provided to secure the glide ball at different threaded positions along the stud to adjust cutting height. Moreover, the structure shown is incompatible with conventional bump feed mechanisms.
U.S. Pat. No. 5,367,862 describes a ground guide attachment for a trimmer head in the form of a saucer-like disk having an upturned circumferential lip and a centrally located mounting post extending upward from the disk for attachment to an existing trimmer head. The mounting post, which is threaded at its remote end, is intended to be inserted through an axial bore in the cord spool and through a receiving hole in an upper support panel of the trimmer head housing, and secured with a nut apparently fixed to an upper support panel of the housing. This construction suffers the same drawbacks mentioned above with respect to U.S. Pat. No. 4,483,069, namely lack of height adjustability and lack of compatibility with conventional bump feed mechanisms.
A different style of ground guide system for automated trimmers is disclosed in U.S. Pat. No. 5,402,627. This patent teaches an elongated support ski having an upwardly extending slotted wall member at one end thereof. The wall member is adjustably fastened to an L-shaped upper member which in turn is fixed to an outer surface of a trimmer head housing. While the disclosed ground guide system is designed for cutting height adjustment, it prevents use of a conventional bump feed mechanism. In addition, the disclosed configuration is susceptible to clogging as cut vegetation accumulates on the wall member.
Another ground guide system offered for sale by Hoffco, Inc. of Richmond, Ind. under the trademark Ground Guard includes a wire surrounding the trimmer head in a generally vertical transverse plane to form side and bottom barriers around the trimmer head. A sliding handle must be operated by the user to raise and lower the wire guard to permit use of a bump feed mechanism. The configuration presents the opportunity for vegetation to accumulate on the wire and plug the trimmer head, and is not height-adjustable.